From owner-svn-src-all@FreeBSD.ORG Thu Apr 2 20:25:39 2015 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id BFAD1CF; Thu, 2 Apr 2015 20:25:39 +0000 (UTC) Received: from mail.turbocat.net (mail.turbocat.net [IPv6:2a01:4f8:d16:4514::2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 74043EB5; Thu, 2 Apr 2015 20:25:39 +0000 (UTC) Received: from laptop015.home.selasky.org (cm-176.74.213.204.customer.telag.net [176.74.213.204]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.turbocat.net (Postfix) with ESMTPSA id 1A4B01FE022; Thu, 2 Apr 2015 22:25:35 +0200 (CEST) Message-ID: <551DA5EA.1080908@selasky.org> Date: Thu, 02 Apr 2015 22:26:18 +0200 From: Hans Petter Selasky User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Robert Watson Subject: Re: svn commit: r280971 - in head: contrib/ipfilter/tools share/man/man4 sys/contrib/ipfilter/netinet sys/netinet sys/netipsec sys/netpfil/pf References: <201504012226.t31MQedN044443@svn.freebsd.org> <1427929676.82583.103.camel@freebsd.org> <20150402123522.GC64665@FreeBSD.org> <20150402133751.GA549@dft-labs.eu> <20150402134217.GG64665@FreeBSD.org> <20150402135157.GB549@dft-labs.eu> <1427983109.82583.115.camel@freebsd.org> <20150402142318.GC549@dft-labs.eu> <20150402143420.GI64665@FreeBSD.org> <20150402153805.GD549@dft-labs.eu> <551D8143.4060509@selasky.org> <551D8945.8050906@selasky.org> <8900318B-8155-4131-A0C3-3DE169782EFC@FreeBSD.org> <551D8C6C.9060504@selasky.org> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Mateusz Guzik , Ian Lepore , svn-src-all@freebsd.org, src-committers@freebsd.org, Gleb Smirnoff , svn-src-head@freebsd.org X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 02 Apr 2015 20:25:39 -0000 On 04/02/15 20:46, Robert Watson wrote: > On Thu, 2 Apr 2015, Hans Petter Selasky wrote: > >>>> Does somebody here know what happens in these two cases: >>>> >>>> If we are transmitting using TSO, will the network adapter increment >>>> the IP ID field somehow? What happens if an outgoing IP packet >>>> resulting from a TSO packet get fragmented by a router? >>> >>> Quite possibly -- this is presumably specified by the NIC vendor, but >>> it would be good to do a bit of a survey and see what happens in >>> practice. >>> >>>> In ip_fragment() when we create fragments we should increment the >>>> ip_id value for each fragment? >> >> I'm asking because the code in FreeBSD, since the beginning probably, >> just copies the IP header, and use the same IP ID for all the >> fragments ! This just hit my mind after some recent work in this area. > > I honestly cannot believe you are proposing that. > > Please go read about how IP fragmentation works. Having an identical IP > ID in ip_fragment() is the point of the function! > Hi, rwatson: You're right, the more fragment flag gets set there, I overlooked that bit. Sorry. glebius: Given that you admit there is a small chance of an IP ID collision in the previous e-mails exchanged in this thread, why don't we have checks for that in ip_reass() when receiving fragmented IP packets? For example when ip->ip_off == 0 we know the TCP and/or UDP port numbers for TCP and UDP payloads and can check if a new fragment is starting before the previous one is completed. Then we would know if a collision has happened and could discard that packet. Not ideal, but better than data corruption. --HPS